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(CNN)One of Aung San Suu Kyi's closest allies has resigned from an international advisory board calling it a "cheerleading squad for government policy" that's failing to address the Rohingya crisis.

In a scathing statement released Thursday, Bill Richardson, the former US ambassador to the UN, accused Suu Kyi -- Myanmar's de facto leader, who he's known for decades -- of lacking "moral leadership."

"It appears that the Board is likely to become a cheerleading squad for government policy as opposed to proposing genuine policy changes that are desperately needed to assure peace, stability and development in Rakhine State," Richardson said.

As of August last year, more than 688,000 Rohingya have been forced to flee their homes in northern Rakine State amid widespread reports of military-backed mass rape, murder and the burning down of entire villages.

The UN and the US have labeled the violence against the mainly Muslim Rohingya as "ethnic cleansing."

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Richardson said that after three days of advisory board meetings it had "become clear that I cannot in good conscience serve in this role."

"In the advisory board's initial meeting with (Suu Kyi), I was taken aback by the vigor with which the media, the United Nations, human rights groups, and in general the international community were disparaged."

"While it is important to recognize that the military still wields significant power and that they are primarily to blame for the recent exodus of refugees in the wake of (Rohingya militant group) ARSA attacks, the absence of (Suu Kyi's) moral leadership on this critical issue is of great concern."

Myanmar government spokesman Zaw Htay told CNN "we are very sorry about Mr Richardson's resignation," and denied accusations Suu Kyi believes there is a concerted international effort against Myanmar. "That is not true," said Htay.

#Myanmar: Bill Richardson, one of 5 international members of the Advisory Board on Rakhine State has resigned. His statement leaves no doubt about his grave concern about the lack of seriousness with which implementation of the recommendations of the Annan report is being pursued pic.twitter.com/paKV5tH0x3

'Furious' response

The resignation of Richardson will come as a blow to both the reputation of the international panel and Suu Kyi herself.

The former democracy fighter and Nobel Peace Prize laureate has come in for intense criticism since the Rohingya crisis intensified last year, but has retained many defenders, particularly in Washington, where she is seen as a vital part of the country's shift to democracy and tilt towards the US and away from China.

During Suu Kyi's years-long house arrest under the junta, Richardson was one of the first westerners to visit her, and had maintained a friendship with her for "decades," he said.

"I was extremely upset at (Suu Kyi's) reaction to my request that she address the situation of the two Reuters journalists both swiftly and fairly," Richardson said, a request he said sparked a "furious" response from Suu Kyi.

Zaw Htay acknowledged Richardson raised the journalists' case in a meeting, but said it "was not relevant to the agenda of the meeting."

"The meeting was only about the issue in Rakhine State," he said. "(Suu Kyi) told Mr Richardson to keep to the correct agenda."

'Lack of a formal mandate'

While the commission's report did not go so far as current UN officials, who have said the situation in Myanmar represents a "textbook case of ethnic cleansing," it did criticize the military and call on the government to take urgent concerted action.

Myanmar officials have pointed to the report as evidence they are being transparent in their handling of the situation in Rakhine, but in a widely-publicized speech on the issue, Suu Kyi directly contradicted several of Annan's findings, and few of the recommendations have yet been implemented.

Richardson criticized the chairman of the advisory board, former Thai deputy prime minister Surakiart Sathirathai, for not being "genuinely committed" to implementing the Annan commission's findings.

"He parroted the dangerous and untrue notion that international NGOs employ radicals and that humanitarian agencies are providing material support to ARSA," said Richardson.

"The advisory board's lack of a formal mandate and Surakiart's general desire to avoid the real issues at the risk of confronting our Myanmar hosts, led to an agenda devoid of any meaningful engagement."

Neither Surakiart nor any other members of the advisory board could be immediately reached for comment.